But many sweet flowers do not readily yield an essential oil, so in such oases we have to rely altogether upon more or less successful substitutes. For instance, the perfumes sold under the names of "heliotrope," "lily of the valley," "lilac," "cyclamen," "honeysuckle," "sweet pea," "arbutus," "mayflower" and "magnolia" are not produced from these flowers but are simply imitations made from other essences, synthetic or natural. Among the "thousand flowers" that contribute to the "Eau de Mille Fleurs" are the civet cat, the musk deer and the sperm whale. Some of the published formulas for "Jockey Club" call for civet or ambergris and those of "Lavender Water" for musk and civet. The less said about the origin of these three animal perfumes the better. Fortunately they are becoming too expensive to use and are being displaced by synthetic products more agreeable to a refined imagination. The musk deer may now be saved from extinction since we can make tri-nitro-butyl-xylene from coal tar. This synthetic musk passes muster to human nostrils, but a cat will turn up her nose at it. The synthetic musk is not only much cheaper than the natural, but a dozen times as strong, or let us say, goes a dozen times as far, for nobody wants it any stronger. Such powerful scents as these are only pleasant when highly diluted, yet they are, as we have seen, essential ingredients of the finest perfumes. For instance, the natural oil of jasmine and other flowers contain traces of indols and skatols which have most disgusting odors. Though our olfactory organs cannot detect their presence yet we perceive their absence so they have to be put into the artificial perfume. Just so a brief but violent discord in a piece of music or a glaring color contrast in a painting may be necessary to the harmony of the whole.